And I'm Steve Inskeep. Federal regulators have unveiled the final version of what has come to be called the Volcker Rule. It's a big part of the financial reform that went into affect three years ago. It's taken all those years to come up with the language that will set new limits on the kinds of trading that banks can do and cannot do. NPR's Jim Zarolli joins us now to talk about this. Hi Jim.

JIM ZAROLLI, BYLINE: Hi.

INSKEEP: So, now that they've got the language, what does the Volcker rule supposed to do?

ZAROLLI: Well, um - it is supposed - it really spells out, in a lot of detail, what kind of activity the banks are allowed to do. For instance, one of the aims of the rule is to borrow what's called portfolio hedging, and this is when banks engage in hedging, or protecting themselves against risk in a really broad range of assets. It's the kind of trading led to the London Whale Incident when traders at JPMorgan Chase made these huge speculative bets and lost 6 billion dollars. I mean, the rule says, you know, banks can hedge, but the hedging has to be tied to specific assets. There has to be limits to it.

INSKEEP: Specific assets, meaning that you have to put your money on something tangible - that you can see, that you can feel - it can't be one of these hedge funds where it's based on a derivative of something, based on a derivative of something else.

ZAROLLI: Well, I mean - I think it means they have to specify, you know, what specifically it's tied to - what assets, you know, what this is being done for. They can't just do it in a wide portfolio of assets.

INSKEEP: So that is the Volcker Rule, or at least the notion of the Volcker Rule, at base, is making sure that banks, since they're holding our money that we deposit, that they make reasonable safe investments - is that the bottom line?

ZAROLLI: Yeah, and it was - the idea was proposed by Paul Volcker, the former Federal Reserve chairman, in 2009. He was really worried about a couple of things that he said could wreak havoc on the financial system. I mean, he was worried about banks doing proprietary trading with federally insured money. In other words, buying and selling assets for their own portfolios. He said banks shouldn't be allowed to do this with money that was guaranteed by tax payers. And then he also wanted to just bar certain kinds of speculative activity all together, like owning private equity funds. He said - so he said placing limits on these kinds of activities was necessary, it would make the system safer overall.

INSKEEP: Why did it take 900 pages to say that, since that is the length of the rule, apparently?

ZAROLLI: Well, this was a - you know, this was a very complicated task, as a lot of behind the scenes wrangling. You know, by its very nature it's kind of hard to spell out when trading is legitimate and when it's not. I mean, if a bank is doing a big trade, is it doing it because it's legitimately trying to hedge against risk or it just trying to make a lot of money. I mean, it's not so easy to tell, sometimes, and the regulators had to differentiate between the things banks can do for their clients and do for themselves, for their own portfolios. The banks are allowed to do certain kinds of trading on behalf of their clients that they can't do for themselves.

INSKEEP: Is this going to add difficulty, in and of itself, simply because of the complexity of this?

ZAROLLI: Well, yeah, I mean I think you can expect that, over time, banks are going to be looking for loopholes in this. I think if you talk to consumer activists, they say the real question is how aggressively our regulators in the future are going to be trying to push back against those kinds of loopholes, and we'll have to wait and see.